/*
cdecoder.c - c source to a base64 decoding algorithm implementation

This is part of the libb64 project, and has been placed in the public domain.
For details, see http://sourceforge.net/projects/libb64
*/

#include "cdecode.h"

int base64_decode_value(char value_in) {
    static const char decoding[] = {
        62, -1, -1, -1, 63, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1,
        -1, -1, -2, -1, -1, -1, 0,  1,  2,  3,  4,  5,  6,  7,  8,  9,
        10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25,
        -1, -1, -1, -1, -1, -1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35,
        36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51};
    static const char decoding_size = sizeof(decoding);
    value_in -= 43;
    if (value_in < 0 || value_in >= decoding_size)
        return -1;
    return decoding[(int)value_in];
}

void base64_init_decodestate(base64_decodestate *state_in) {
    state_in->step = step_a;
    state_in->plainchar = 0;
}

int base64_decode_block(const char *code_in, const int length_in,
                        char *plaintext_out, base64_decodestate *state_in) {
    const char *codechar = code_in;
    char *plainchar = plaintext_out;
    char fragment;

    *plainchar = state_in->plainchar;

    switch (state_in->step) {
        while (1) {
        case step_a:
            do {
                if (codechar == code_in + length_in) {
                    state_in->step = step_a;
                    state_in->plainchar = *plainchar;
                    return (int)(plainchar - plaintext_out);
                }
                fragment = (char)base64_decode_value(*codechar++);
            } while (fragment < 0);
            *plainchar = (fragment & 0x03f) << 2;
        case step_b:
            do {
                if (codechar == code_in + length_in) {
                    state_in->step = step_b;
                    state_in->plainchar = *plainchar;
                    return (int)(plainchar - plaintext_out);
                }
                fragment = (char)base64_decode_value(*codechar++);
            } while (fragment < 0);
            *plainchar++ |= (fragment & 0x030) >> 4;
            *plainchar = (fragment & 0x00f) << 4;
        case step_c:
            do {
                if (codechar == code_in + length_in) {
                    state_in->step = step_c;
                    state_in->plainchar = *plainchar;
                    return (int)(plainchar - plaintext_out);
                }
                fragment = (char)base64_decode_value(*codechar++);
            } while (fragment < 0);
            *plainchar++ |= (fragment & 0x03c) >> 2;
            *plainchar = (fragment & 0x003) << 6;
        case step_d:
            do {
                if (codechar == code_in + length_in) {
                    state_in->step = step_d;
                    state_in->plainchar = *plainchar;
                    return (int)(plainchar - plaintext_out);
                }
                fragment = (char)base64_decode_value(*codechar++);
            } while (fragment < 0);
            *plainchar++ |= (fragment & 0x03f);
        }
    }
    /* control should not reach here */
    return (int)(plainchar - plaintext_out);
}
